1. Field of the Invention
This invention is in the field of integrated circuits, and is more specifically directed to the application of copper.
2. Description of the Prior Art
In contemporary fabrication of integrated circuits, interconnect usually is formed by metal. Available metals for interconnect must satisfy some requirements such as low resistivity, high resistance to electromigration failure effects, excellent adhesion to underlying substrate material and low film stress, etc.
Among all of the available metals, aluminum is most widely used in the contemporary manufacture of silicon integrated circuits. Advantages of aluminum include low resistivity (2.7 .mu..OMEGA.-cm) and good adhesion to silicon dioxide and silicon.
As device dimensions continue to scale down, however, some disadvantages of aluminum such as relatively poor resistance to electromigration effects and corrosion become a bottleneck, and then it is necessary to find other metal for the interconnect.
Because copper has low resistivity (1.7 .mu..OMEGA.-cm) and good electromigration resistance, it would thus be a processing interconnect material, especially when device dimensions approach deep-submicron sizes.
However, copper could rapidly diffuse into surrounding dielectric materials, especially into silicon dioxide, due to its nature. Thus, it is necessary to inhibit this diffusion by a diffusion barrier layer to render certainly real profile of copper connect, similar to the desired profile of copper connect. As usual, the diffusion barrier layer is provided by silicon nitride layer which is formed by a plasma enhanced chemical vapor deposition (PECVD) process.
There are, in principal, still two issues about the application of copper and silicon nitride. First, silicon nitride has poor adhesion to copper surfaces, resulting in the peeling of the silicon nitride from the copper surface. Second, copper is easy to be oxidized and then an additional process is required to remove the unwanted copper oxide layer.
Accordingly, it is necessary to overcome these issues to take advantages of the copper connect. Especially when the chemical mechanical polishing process is broadly used to remove excess copper, the lack of properly dry etching does not restrict the application of copper.